January 22, 2026

Noninferiority of One HPV Vaccine Dose to Two Doses
A total of 20,330 participants were enrolled and underwent randomization, and 3005 unvaccinated participants were enrolled. Girls 12 to 16 years of age were randomly assigned, in a 1:1:1:1 ratio, to receive one or two doses of a bivalent HPV vaccine or one or two doses of a nonavalent HPV vaccine. The primary end point was new HPV type 16 or 18 infection occurring from month 12 to month 60 and persisting for at least 6 months. They assessed vaccine effectiveness by comparing HPV16 or HPV18 infection among the trial participants. The noninferiority analysis showed that one vaccine dose was noninferior to two doses in preventing HPV16 or HPV18 infection. The rate difference between one and two doses of the bivalent vaccine was −0.13 infections per 100 participants (95% confidence interval [CI], −0.45 to 0.15; P<0.001 for noninferiority), and the difference between one and two doses of the nonavalent vaccine was 0.21 infections per 100 participants (95% CI, −0.09 to 0.51; P<0.001 for noninferiority). The vaccine effectiveness was at least 97% in each of the four trial groups. No safety concerns were identified. 

Herd Effect of Human Papillomavirus Vaccination on Incidence of High-grade Cervical Lesions: A Population-based Cohort Study in Sweden 
These are the results of a nationwide, retrospective, register-based cohort study including 857,168 girls and women born between 1985 and 2000, using data from the Swedish National Cervical Screening Registry and several national health and population registries. Participants were grouped by birth cohorts exposed to different HPV vaccination strategies: opportunistic vaccination (1985–88; reference group), subsidised vaccination (1989–92), catch-up vaccination (1993–98), and school-based vaccination (1999–2000). Participants were followed up from age 10 years or from Jan 1, 2006, whichever came later, until their first HPV dose, a (high-grade cervical lesion) HSIL+ diagnosis, emigration, death, their 35th birthday, or Dec 31, 2022. Authors identified 42,274 cases of HSIL+, with cumulative incidence differing across birth cohorts and lowest in the 1999–2000 cohort. For participants aged 23 years, with the 1985–88 cohort as the reference group, the IRR of HSIL+ was 0·53 (95% CI 0·39–0·73) in the 1999–2000 cohort, 1·26 (1·19–1·34) in the 1993–98 cohort, and 1·26 (1·18–1·34) in the 1989–92 cohort. IRRs in the older cohorts were reduced with increased age, declining to 1·00 (0·87–1·05) by the age of 29 years for the 1993–98 cohort and 0·89 (0·80–0·99) by the age of 33 years for the 1989–92 cohort. HSIL+ incidence in unvaccinated women declined in the birth cohort eligible for HPV vaccination through a school-based programme. This finding shows that the herd effect can be achieved through high-coverage HPV vaccination.